1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of monosaccharides. More specifically, the invention relates to a process for separating arabinose from a mixture comprising arabinose and one or more additional pentoses and/or hexoses, which process employs an adsorbent comprising a crystalline aluminosilicate to selectively adsorb arabinose from the feed mixture.
2. Description of the Prior Art
The use of crystalline aluminosilicates to perform hydrocarbon separation is well known in the separation art. Examples of such separatioqs are disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491 wherein a type A zeolite is used to separate normal paraffins from branched chain paraffins. The use of faujasites to separate olefinic hydrocarbons from paraffinic hydrocarbons is described in U.S. Pat. Nos. 3,265,750 and 3,510,423.
In non-hydrocarbon separations it is also known that zeolites can be used to separate specific monosaccharides or classes of monosaccharides from carbohydrate feed mixtures. A specific example of a class separation is given in U.S. Pat. No. 4,024,331 disclosing the separation of ketoses from a mixture of ketoses and aldoses using a type X zeolite. Specific monosaccharides such as glucose and fructose are isolated from a feed mixture containing the same by an adsorptive separation process using an X zeolite as taught in U.S. Pat. No. 4,442,285.
This invention is particularly concerned with the separation of arabinose from other monosaccharides. Obtaining pure arabinose has commercial significance in light of its potential as a starting material for the production of L-glucose, a possible nonnutritive sweetener. A common source of arabinose is the hydrolysis of hemicellulose in making pulp from wood or as a product of the conversion of plant tissue to sugars in biomass operations. Regardless of the source, the arabinose is typically found in a mixture of many monosaccharides. Therefore, it is highly desirable to have a simple method for separating arabinose from the other monosaccharides present in the source mixture. However, in light of the ultimate food use of arabinose, the separation process must not provide contaminants that will render the arabinose or subsequent products unsuitable for human consumption.
Specific methods for separating arabinose are known in the art. U.S. Pat. No. 3,160,624 discloses the separation of D(L)-arabinose from D(L)-ribose by chromatography using a cellulose powder or ion exchanged resin. However, it is well known in the art that resin or cellulose adsorbents pose significant operational problems when their use is attempted on a large scale due to the high pressure drops associated with their use. The zeolite adsorbents which are commonly used in large scale adsorptive separation processes have also been applied to the separation of arabinose from other mixtures of monosaccharides. European Patent Application EP No. 115,068 is directed to the separation of L-arabinose from a mixture of sugar that exists in the hydrolyzates of wood and beet pulp. In the European application, an X type zeolite exchanged with barium cations is disclosed as an adsorbent. Due to the toxic properties of barium, this separation process will be difficult to apply when attempting to obtain food grade arabinose.
Additional data related to potential adsorbents for the separation of mannose from other monosaccharides is set forth in U.S. Pat. No. 4,471,114. This patent contains data related to the use of a Y type faujasite containing calcium cations as an adsorbent for the separation of mannose from other monosaccharides.
In contradistinction to these findings, it has been discovered that faujasites containing calcium ions at cation exchanged sites are suitable adsorbents for the separation of arabinose from other monosaccharide aldoses. Moreover, the use of these zeolites with calcium cations allows the purification of arabinose in a process that is acceptable for the food industry.